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91-09-27.DLY
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1991-09-27
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/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
DAILY SUMMARY OF SOLAR GEOPHYSICAL ACTIVITY
27 SEPTEMBER, 1991
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
(Based In-Part On SESC Observational Data)
SOLAR AND GEOPHYSICAL ACTIVITY INDICES FOR 27 SEPTEMBER
-------------------------------------------------------
!!BEGIN!! (1.0) S.T.D. Solar Geophysical Data Broadcast for DAY 270, 09/27/91
10.7 FLUX=177.9 90-AVG=202 SSN=173 BKI=3556 3542 BAI=036
BGND-XRAY=C1.0 FLU1=2.9E+05 FLU10=8.3E+03 PKI=5555 4443 PAI=038
BOU-DEV=035,072,090,122,037,076,057,016 DEV-AVG=063 NT SWF=00:000
XRAY-MAX= C8.5 @ 0355UT XRAY-MIN= B8.6 @ 2355UT XRAY-AVG= C1.7
NEUTN-MAX= +003% @ 0940UT NEUTN-MIN= -002% @ 1050UT NEUTN-AVG= +0.3%
PCA-MAX= +0.5DB @ 1420UT PCA-MIN= -0.1DB @ 1610UT PCA-AVG= +0.2DB
BOUTF-MAX=55317NT @ 0315UT BOUTF-MIN=55251NT @ 0857UT BOUTF-AVG=55292NT
GOES7-MAX=E:+148NT@ 0456UT GOES7-MIN=N:-058NT@ 0900UT G7-AVG=+067,+075,+001
GOES6-MAX=P:+137NT@ 0907UT GOES6-MIN=E:-036NT@ 0705UT G6-AVG=+074,+009,+029
FLUXFCST=STD:185,195,200;SESC:190,200,210 BAI/PAI-FCST=025,020,015/032,025,025
KFCST=3556 6433 4555 4434 27DAY-AP=041,035 27DAY-KP=5554 4454 4565 4322
WARNINGS=*MAJFLR;*GSTRM;*AURMIDWRN
ALERTS=**TENFLR:210SFU@0353,DUR:1;**MINSTRM
!!END-DATA!!
BRIEF SUMMARY OF EVENTS
-----------------------
Solar activity became low today. Region 6848 (S07E27) grew over the
last 24 hours. An area of emerging flux has begun to appear near the
trailing edge of Region 6848, between this region and Region 6850 (S11E44).
The area where this new flux is emerging is already visibly contorted in
Hydrogen Alpha light, possibly a result of the subsurface fields associated
with the emerging flux. Interaction between Region 6848, 6850 and the area
of emerging flux may prove to be a source for potential future activity.
Region 6850 is a large and complex solar region with the potential for
spawning powerful solar energetic events. This region has continued to grow
steadily since becoming visible on the southeast limb several days ago.
Optically, this region is the largest and most complex that can be rated (an
FKC optical group). Magnetically, this region is categorized as a
beta-gamma-delta group, which is also the most potent magnetic configuration
for sunspot groups. An inversion line runs on a near north-south axis
between the main leader and follower spots. This line does not appear to be
very strongly sheared at the present time, which is probably part of the
reason the group has been so stable. However, the group could be
destabilized quite rapidly should new flux begin to emerge near or within
this region. The penumbral extent of this large region is most impressive in
white-light.
Region 6853 (S20E56), although much smaller than Region 6850, produced
most of todays flare activity. Included in the activity was a C8.5/SF
tenflare of 210 sfu at 03:55 UT and a long duration C7/SF event at 16:23 UT.
The only other notable events were filament disappearances. Two
segments of filament, one located near N15E48 and the other located near
S20E12, disappeared sometime during the day.
No new solar regions were assigned today, although there is a chance
that the emerging flux between Region 6850 and 6848 may deserve a number of
its own if growth continues.
Solar activity should become moderate. There is ample complexity in the
southeast regions to expect minor M-class flare activity. There is also
a moderate risk for a major M or X-class flare from Region 6850 should it
destabilize during the period. At the present time, we see no signs of
destabilization, although this can happen quite rapidly and unexpectedly.
Region 6850 is capable of producing proton flares. Although it is not yet in
a particularly favorable position for producing near-Earth proton
enhancements, a slight risk does exist should an energetic event erupt from
this region over the next 24 hours. This region will cross the central
meridian on 01 October. It will be treated as a potentially high-threat
region after 29 September (inclusive).
Geomagnetic activity ranged from unsettled to severe storm levels today.
Severe geomagnetic storming occurred between 08:00 UT and 12:00 UT over the
high latitude regions on 27 September. Middle latitudes observed periods of
major geomagnetic storming during the same period. The solar coronal hole
which has been producing this storm activity is beginning to move out of
influential range. Storming should begin to let up later in the UT day
(after 15:00 UT) on 28 September. A return to generally unsettled to active
levels should be observed on 29 or 30 September (barring possible major solar
energetic events).
Auroral activity became high over the high latitude regions on 27
September associated with the major to severe storm periods. Despite the
auroral storming which has occurred, lunar phase has strongly inhibited
attempts to view activity. Lunar phase will begin to become less of an
observational inhibitor over the next several days. However, the decline in
storm activity will keep activity confined mostly to the northerly middle and
high latitude regions. The Middle Latitude Auroral Activity Warning will
probably be downgraded to a Watch within the next 24 hours.
HF propagation conditions have been below normal over most regions.
Low latitude paths had almost normal conditions throughout the period, while
middle latitude paths suffered from storm-related effects (ex. fading,
flutter and increased noise and absorption). High and polar latitude paths
suffered fairly strong degradation throughout the day, with generally poor to
very poor propagation conditions reported. A slight increase in PCA (Polar
Cap Absorption) was observed today which (together with a slightly expanded
polar cap region due to storming) contributed to further degradation of polar
and high latitude signal paths. Conditions should begin to show some
improvement over the next 24 to 48 hours as geomagnetic and auroral activity
begin to wane (barring possible major solar energetic events).
** End of Daily Update **